The network interface addresses that this mail system receives mail on. Specify "all" to receive mail on all network interfaces (default), and "loopback-only" to receive mail on loopback network interfaces only (Postfix version 2.2 and later). The parameter also controls delivery of mail to user@[ip.address].

Note 1: you need to stop and start Postfix when this parameter changes.

Note 2: address information may be enclosed inside [], but this form is not required here.

When inet_interfaces specifies just one IPv4 and/or IPv6 address that is not a loopback address, the Postfix SMTP client will use this address as the IP source address for outbound mail. Support for IPv6 is available in Postfix version 2.2 and later.

On a multi-homed firewall with separate Postfix instances listening on the "inside" and "outside" interfaces, this can prevent each instance from being able to reach servers on the "other side" of the firewall. Setting smtp_bind_address to 0.0.0.0 avoids the potential problem for IPv4, and setting smtp_bind_address6 to :: solves the problem for IPv6.

A better solution for multi-homed firewalls is to leave inet_interfaces at the default value and instead use explicit IP addresses in the master.cf SMTP server definitions. This preserves the Postfix SMTP client's loop detection, by ensuring that each side of the firewall knows that the other IP address is still the same host. Setting $inet_interfaces to a single IPv4 and/or IPV6 address is primarily useful with virtual hosting of domains on secondary IP addresses, when each IP address serves a different domain (and has a different $myhostname setting).

See also the proxy_interfaces parameter, for network addresses that are forwarded to Postfix by way of a proxy or address translator.

Note 1: when inet_interfaces specifies no more than one IPv4 address, and that address is a non-loopback address, it is automatically used as the smtp_bind_address. This supports virtual IP hosting, but can be a problem on multi-homed firewalls. See the inet_interfaces documentation for more detail.

Note 2: address information may be enclosed inside [], but this form is not required here.